The present invention broadly relates to a heated controlled deflection roll and, more specifically, pertains to a roll or roller comprising a roll shell or jacket which is rotatable about a nonrotatable or stationary support or beam and supported with respect to the latter by means of at least one support or pressure element, and at least one device for heating the inner side of the roll shell or jacket. The present invention also relates to a new and improved method of operating the inventive roll or roller.
Such rolls or rollers are preferably used for surface treatment or finishing of material webs, particularly of fibrous material such as paper, paperboard, nonwovens, textile or plastic material, under the simultaneous action of pressure and heat. Such rolls or rollers are particularly suitable for smoothing paper webs in glazing roll stacks or calenders, in which case the paper fibers are more readily plasticizable by virtue of a higher operating temperature and a smoothing or glazing effect at the paper surface is rendered possible under the action of pressure.
Controlled deflection rolls, also known in the art as rolls with bending or sag compensation, in which the rotating roll shell or jacket is supported with respect to the nonrotatable support or beam by means of at least one support element, for example, by means of at least one pressure chamber or a row of hydraulic or other support elements, have proven to be especially suitable for obtaining a uniform pressing force or a pressing force with a desired force or pressure profile over the entire roll width, as well as for attaining a uniform heat transfer from the roll or roller surface to the material web or, alternatively, a heat transfer regulated according to a desired profile of surface heat passage or transfer over the entire roll width, in other words, in the cross-machine direction.
This is particularly advantageous in the case of large roll widths up to the range of 10 meters, such roll widths being customary in papermaking machines.
Heatable controlled deflection rolls of the above type are disclosed, for example, in U.S. Pat. No. 4,282,638, granted Aug. 11, 1981 and comprise spray devices laterally secured to the stationary roll support, liquid spray jets of a heat carrier-liquid emanating from such spray devices during operation. In this manner, the roll shell or jacket is heated by means of flow-impact heating.
On the other hand, controlled deflection rolls known, for example, from Swiss Patent No. 577,598, published July 15, 1976 and U.S. Pat. No. 4,282,639, granted Aug. 11, 1981 comprise a row of hydrostatic pressure or support elements, the bearing surfaces of which are provided with bearing pockets or recesses which are supplied with heated hydraulic pressurized fluid medium via throttle bores and related cylindrical bores which are flow connected with a central bore provided in the stationary support, this central bore being connected with a source of hydraulic pressurized fluid medium. In this manner, the inner side of the roll shell or jacket is heated by the hot hydraulic pressurized fluid medium.
These known rolls or rollers have the disadvantage that the heating of the roll shell or jacket is effected by means of a heat carrier-fluid. Since practically the entire interior of the roll is heated, a considerable loss of thermal energy occurs, so that only a smaller portion of the supplied energy is actually used for heating the roll shell or jacket. In addition, the heat-up time for such rolls or rollers to reach the required operating temperature is frequently too long for the start-up phase of the glazing roll stack or calender, so that no effective and economical operation is rendered possible.
It is further disadvantageous that the working or processing temperature, which can be obtained by these known rolls or rollers at the surface thereof, is restricted or limited, because the components located within the roll or roller and required for supplying the heating fluid medium as well as the heating oil itself can only be employed up to a certain temperature limit.
Furthermore, during the heat-up phase of such controlled deflection rolls there can arise high tensile stress at the inner side of the roll shell or jacket. Such tensile stress can even lead to bursting of the roll shell or jacket and, so far, could not be eliminated.
Instead of heating the roll or roller from within, the suggestion has been made to provide an exterior heating which acts upon the outer surface of the roll shell or jacket. A considerable loss of energy occurs thereby and likewise there arise irregularities of heat transfer which can lead to destruction of the roll shell or jacket during the heat-up phase. Rolls or rollers which contain a chilled-cast-iron shell or jacket customary in glazing roll stacks and calenders have proven to be especially sensitive in this respect, whereby the manufacturing process of such shells or jackets already results in a certain inherent or internal stress in the outer skin of the shell or jacket.